Paint composition for automotive weather strip and glass run, and process for producing automotive weather strip and glass run

ABSTRACT

A paint composition for automotive weather strips and glass runs which comprises a curable urethane-based emulsion paint having added thereto either at least two silane coupling agents selected from the group consisting of a silane coupling agent having an amino group, a silane coupling agent having an epoxy group, a silane coupling agent having a methacryloxy group and a silane coupling agent having an acryloxy group, or a reaction product obtained by previously mixing said at least two silane coupling agents. Also discloses are processes for producing automotive weather strips.

This is a divisional of application Ser. No. 09/810,616 filed Mar. 19,2001 now U.S. Pat. No. 6,590,027; the disclosure of which isincorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to a paint composition for automotiveweather strips and glass runs, as well as processes for producingautomotive weather strips and glass runs.

BACKGROUND OF THE INVENTION

Most automotive weather strips and glass runs (which are hereundersometimes referred to simply as “automotive weather strips”) are coatedwith curable urethane-based paints on the surface of the substrate toimpart it special functions such as wear resistance and slip property(sliding property) or provide it with better appearance.

Conventionally, curable urethane-based paints of a solvent type havebeen used in the manufacture of automotive weather strips; however, withthe recent concern over the global environment and the health of workingpersonnel, a need has arisen for a shift toward aqueous and other paintsof a non-solvent type.

However, water which is the medium for paints of the aqueous type havemore latent heat of evaporation than solvents, so the aqueous paintsrequire more heat than paints of the solvent type in order to dry up thewater after application. In addition, unlike solvent-type paints thatallow adjustment of volatilization temperature and rate by combiningseveral kinds of solvents, aqueous-type paints require preliminarydrying in order to prevent “flashing” due to nearly instantaneousvolatilization of water. As a result, longer drying times are requiredby the aqueous paints and in order to deal with this low productivityproblem, it becomes necessary to build a new drying oven for shiftingfrom the solvent-type paint to the aqueous type.

Most automotive weather strips use substrates that are made ofthermosetting elastomers such as EPDM rubber (ethylene propylene rubber)or thermoplastic elastomers such as TPO (thermoplastic polyolefins).

If thermoplastic elastomers are used as the substrate, drying should becarried out at a low temperatures of 150° C. or below to prevent thermaldeformation that would otherwise occur during post-application drying;however, if the paint applied is of the aqueous type, the dryingoperation is not highly productive since water is very difficult to dry.

The EPDM rubber as an exemplary thermosetting elastomer is nonpolar andhas low sticking property and it is also hydrophobic; hence, aqueouspaints cannot produce a more adhesive coat than solvent-type paints.

With a view to solving this problem, pretreatments such as coronadischarge and primer application are conventionally applied to thesubstrate surface but problems still remain, such as high initial costand the difficulty involved in performing positive pretreatments oncomplexly shaped articles.

SUMMARY OF THE INVENTION

Therefore, a first object of the invention is to provide a paint forautomotive weather strips that is free from the above-mentioned defectsof the prior art and which can achieve strong adhesion to the EPDMrubber without corona discharge, primer application or otherpretreatments on the substrate surface while exhibiting high wearresistance.

A second object of the invention is to provide a process for producingautomotive weather strips which does not require the as-applied coat tobe cured completely in a drying oven but which permits it to be curedcompletely by the heat inertia of the drying step and which can alsoshorten the length of the drying oven or lower the drying temperature.

A third object of the invention is to provide a process by whichautomotive glass runs having high wear resistance in the bottom portionwhile exhibiting high softness and flexibility in the lip portions canbe produced efficiently and with minimum impact on the globalenvironment.

As a result of the extensive studies made in order to attain theabove-mentioned objects, the present inventors found that the firstobject of the invention could be attained by adding at least twospecified silane coupling agents or a product of premixing reactionbetween said at least two silane coupling agents to a curableurethane-based emulsion paint.

Thus, in a first aspect, the present invention relates a paintcomposition for automotive weather strips comprising a curableurethane-based emulsion paint having added thereto either at least twosilane coupling agents selected from the group consisting of a silanecoupling agent having an amino group, a silane coupling agent having anepoxy group, a silane coupling agent having a methacryloxy group and asilane coupling agent having an acryloxy group, or a reaction productobtained by previously mixing said at least two silane coupling agents.

The second object of the invention can be attained by a process forproducing automotive weather strips which comprises the steps ofextruding a semi-finished product of automotive weather strip while itis continuously coated with a urethane-based aqueous paint, then dryingand curing the product in a heating furnace, or comprises extruding asemi-finished product of automotive weather strip, heating it,immediately followed by continuous application of a urethane-basedaqueous paint, then drying and curing the product in a heating furnace,or comprises unrolling a semi-finished extruded product of automotiveweather strip while it is continuously coated with a urethane-basedaqueous paint, then drying and curing the extruded product in a heatingfurnace, wherein a silicone compound having an amino group is applied tothe coated surface of the semi-finished product or extruded productafter it leaves the heating furnace, or wherein a silicone compoundhaving an amino group is incorporated in the urethane-based aqueouspaint.

The third object of the invention can be attained by a process forproducing automotive glass runs which comprises the steps of extruding asemi-finished product of automotive glass run as while is continuouslycoated with a silane-crosslinkable polyethylene, then drying and curingthe product in a heating furnace, or comprises the steps of extruding asemi-finished product of automotive glass run, heating it, immediatelyfollowed by continuous coating with a silane-crosslinkable polyethylene,then drying and curing the product in a heating furnace, or comprisesthe steps of unrolling a semi-finished extruded product of automotiveglass run while it is continuously coated with a silane-crosslinkablepolyethylene, each of which processes further comprises applying anurethane resin-based aqueous paint containing a silicone compound havingan amino group or a silicone compound having an amino group or asolution thereof onto the silane-crosslinkable polyethylene coat, thenheating the applied product in a heating furnace to dry and cure theapplied aqueous paint, silicone compound or solution and to crosslinkthe silane-crosslinkable polyethylene.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic representation of an abrasion tester according toa method specified by the Japan Society for Promotion of ScientificResearch;

FIG. 2 is an illustration of a glass run product;

FIG. 3 is an illustration of another type of glass run product; and

FIG. 4 illustrates how a glass run product is subjected to an abrasiontest or a sliding resistance test.

DETAILED DESCRIPTION OF THE INVENTION

The following is the description of a mode for carrying out theinvention as it relates to a paint composition for automotive weatherstrips.

The curable urethane-based emulsion paint which is used as the base ofthe paint composition is a urethane-based emulsion paint which typicallyuses an isocyanate-, melamine-, epoxy- or carbodiimide-based curingagent.

Examples of the silane coupling agent having an amino group includeγ-aminopropyltrimethoxysilane, γ-aminopropyltriethoxysilane andN-β-(aminoethyl)-γ-aminopropyltrimethoxysilane.

Examples of the silane coupling agent having an epoxy group includeγ-glycidoxypropyltrimethoxysilane, γ-glycidoxypropyltriethoxysilane andβ-(3,4-epoxycyclohexyl)ethyltrimethoxysilane.

Examples of the silane coupling agent having a methacryloxy groupinclude γ-methacryloxypropyltrimethoxysilane,γ-methacryloxypropyltriethoxysilane,γ-methacryloxypropylmethyldiethoxysilane and3-acryloxypropylmethoxysilane.

At least two of the silane coupling agents listed above or theirreaction product is preferably added in an amount of 10 to 40 parts byweight per 100 parts by weight of the involatile content in the basecurable urethane-based emulsion paint.

The following is the description of a mode for carrying out theinvention as it relates to a process for producing automotive weatherstrips.

The substrate of automotive weather strips is not limited in anyparticular way but thermoplastic elastomers are preferably used.

The urethane-based aqueous paint may be a urethane-based emulsion paintwhich typically uses an isocyanate-, melamine-, epoxy- orcarbodiimide-based curing agent.

Preferred examples of the silicone compound having an amino groupinclude aminosilane coupling agent such asγ-aminopropyltrimethoxysilane, γ-aminopropyltriethoxysilane andN-β-(aminoethyl)-γ-aminopropyltrimethoxysilane, as well asamino-modified silicone oils.

If the silicone compound having an amino group is to be applied to thecoated surface of the substrate as it emerges from the drying oven, itmay be diluted with water. The application method is in no way limitedand spraying and brushing may be mentioned as typical examples.

The following is the description of a mode for carrying out theinvention as it relates to a process for producing automotive glassruns.

The urethane-based aqueous paint may be a urethane-based emulsion paintwhich typically uses an isocyanate-, melamine-, epoxy- orcarbodiimide-based curing agent.

The silane-crosslinkable polyethylene which is to be applied to thebottom portion of a semi-finished extruded product of automotive glassrun is as easily processable as common polyethylenes before crosslinkingbut, once processed, exhibits better sliding and wear-resistantproperties than ultrahigh molecular-weight polyethylenes; hence, thesilane-crosslinkable polyethylene is suitable for use as a slidingmember in the bottom portions of glass runs that require high wearresistance.

The silane-crosslinkable polyethylene reacts with water and condensesthrough the removal of alcohol to thereby become crosslinked. If theaqueous paint containing the silicone compound having an amino group isapplied to the silane-crosslinkable polyethylene coat, which is thendried and cured in a heating furnace, the water in the aqueous paint andthe silicone compound having an amino group which has a catalytic actionin the condensation of silane crosslinks by removal of alcohol worktogether to cause rapid crosslinking and curing of the appliedsilane-crosslinkable polyethylene coat. The silicone compound having anamino group offers the added advantage of promoting the curing of theas-applied aqueous paint film, thereby increasing its adhesion to theEPDM rubber or silane-crosslinkable polyethylene.

The lip portions of glass runs do not require as high wear resistance astheir bottom portions. On the other hand, they should have bettersealing and handling properties, higher ability to prevent rattlingsound and dust scratching, and more attractive appearance; therefore,the sliding member to be used in the lip portions should not impair thesoftness and flexibility of the substrate rubber and is suitably basedon polyurethane resins.

Preferred examples of the silicone compound having an amino groupinclude aminosilane coupling agents such asγ-aminopropyltrimethoxysilane, γ-aminopropyltriethoxysilane andN-β-(aminoethyl)-γ-aminopropyltrimethoxysilane, as well asamino-modified silicone oils. The silicone compound having an aminogroup is preferably incorporated in amounts ranging from 2 to 15 partsby weight per 100 parts by weight of the involatile content of theaqueous paint.

Coating with the silane-crosslinkable polyethylene may be accomplishedby coextrusion with rubber or it may be applied after vulcanizationwhile the rubber is still hot.

The present invention will now be described by way of reference to theFIGS, which should in no way be construed as limiting the presentinvention. FIG. 1 is a schematic representation of an abrasion testeraccording to a method specified by the Japan Society for the Promotionof Scientific Research, in which D is an abrading glass plate (t=3.5 mm)and E is a coated sample. FIG. 2 is an illustration of a glass runproduct, in which F is a coated site, G is crosslinked PE, and H is EPDMrubber. FIG. 3 is an illustration of another glass run product, in whichF is a coated site and H is EPDM rubber. FIG. 4 illustrates how a glassrun product is subjected to an abrasion test or a sliding resistancetest.

EXAMPLES

The present invention is illustrated in greater detail below withreference to the following Examples, but the invention should not beconstrued as being limited thereto.

Examples 1 and 2 and Comparative Example 1

The data in Table 1 demonstrates the advantages of the paint compositionaccording to the invention. Two samples of a curable urethane polymerwere mixed with two silane coupling agents to prepare two paintcompositions, which were tested for adhesion, wear resistance anddynamic friction coefficient. The results are shown in Table 1 togetherwith those of a comparative paint composition.

TABLE 1 Ex. 1 Ex. 2 Ex. 3 Amount Curable 100.0 100.0 100.0 (parts byurethane wt.) polymer Silane A 8.0 8.0 8.0 Silane B 8.0 — — Silane C —8.0 8.0 Adhesion (N/cm) 7.0 7.0 4.0 Wear resistance 30,000 20,000 10,000(cycles)¹ Dynamic friction ≦0.1 ≦0.1 0.2 coefficient (μK) Silancecoupling agent A: γ-glycidoxypropyltrimethoxysilane (KBM-403 ofShin-Etsu Chemical Co., Ltd.; TSL 8350 of GE Toshiba Silicone; SH-6040of Toray Dow Silicone) Silane coupling agent B:3-acryloxypropyltrimethoxysilane (KBM-5103 of Shin-Etsu Chemical Co.,Ltd.) Silane coupling agent C: γ-aminopropyltrimethoxysilane (KBM-903 ofShin-Etsu Chemical Co., Ltd.; TSL 8330 of GE Toshiba Silicone) ¹Wearresistance: The coated surface was rubbed with a glass plate (seeFIG. 1) until the substrate became exposed. The wear resistance of thesample was evaluated in terms of the number of cycles the glass platewas reciprocated before the substrate showed.

Examples 3 and 4 and Comparative Examples 2 and 3

The data in Table 2 demonstrates the advantages of the process forproducing an automotive weather strip according to the invention.Extruded, heated and later cooled automotive weather strips were coatedwith two samples of urethane-based aqueous paint containingγ-aminopropyltrimethoxysilane as a silicone compound having an aminogroup, thereby preparing weather strip products, which were tested forwear resistance. The results are shown in Table 2 together with those oftwo comparative products.

TABLE 2 Ex. 3 Ex 4 Comp. 2 Comp. 3 Treatment with yes yes no no siliconcompound¹ Drying/curing 200° C. × 80° C. × 200° C. × 80° C. × conditions10 min 10 min 10 min 10 min Wear EPDM 20,000 20,000 10,000 5,000resistance rubber (cycles)² TPO  5,000  5,000  2,000   100 ¹ Siliconecompound: Gamma-aminopropyltrimethoxysilane (KBM-903 of Shin-EtsuChemical Co., Ltd.; TSL 8330 of GE Toshiba Silicone) was processed intoa 10% solution by means of ion-exchanged water. ²Wear resistance: Thecoated surface was rubbed with a glass plate (see FIG. 1) until thesubstrate became exposed. The wear resistance of the sample wasevaluated in terms of the number of cycles the glass plate wasreciprocated before the substrate showed.

Examples 5-7 and Comparative Examples 4-6

The data in Table 3 demonstrates the advantages of the process forproducing a glass run according to the invention. Glass run productsmade using γ-aminopropyltrimethoxysilane as a compound having an aminogroup were tested for wear resistance, resistance to sliding andadhesion to EPDM rubber and crosslinked polyethylene (PE). The resultsare shown in Table 3 together with those of comparative products.

TABLE 3 Ex. 5 Ex. 6 Ex. 7 Comp. 4 Comp. 5 Comp. 6 Amount Curableurethane 100.0 — 100.0 100.0 — 100.0 (parts by polymer wt.) in Silanecoupling 10.0 10.0 10.0 — — — coating film agent¹⁾ (F) Ion-exchangedwater — 90.0 — — — — Wear resistance (cycles)²⁾ 40,000 — 40,000 10,000 —10,000 Sliding resistance 3.0 3.0 5.0 — 5.0 (N/100 mm)³⁾ Adhesion toEPDM rubber_(H)⁴⁾ ◯ — ◯ Δ — Δ Adhesion to cross-linked PE (G)⁴⁾ ◯ ◯ — XX — Glass run product FIG. 1 FIG. 1 FIG. 2 FIG. 1 FIG. 1 FIG. 2 ¹⁾Silane coupling agent: Gamma-aminopropyltrimethoxysilane (KBM-903 ofShin-Etsu Chemical Co., Ltd.; TSL 8330 of GE Toshiba Silicone). ²⁾ Wearresistance: A glass run product (see FIG. 2 or 3) was set on a test jig(see FIG. 4) and a glass plate (100 × 70 mm; t = 3.5 mm) was allowed toslide back and forth until the substrate became exposed in the coatedlip portions and the bottom portion. The wear resistance was evaluatedin terms of the number of cycles the glass plate was reciprocated beforethe substrate showed. ³⁾Sliding resistance: A glass run product (seeFIG. 2 or 3) was set on a test jig (see FIG. 4) and a glass plate (100 ×70 mm, t = 3.5 mm) was allowed to slide for a distance of 70 mm; theresulting resistance was measured. ⁴⁾Adhesion: The coated surface wasrubbed with a calico cloth under a load of 1 kg until either the coattransferred to the cloth or the substrate became exposed. (The criteriafor rating were: ◯, neither transfer to the cloth nor exposure of thesubstrate; X, the substrate became exposed).

As described on the foregoing pages, the paint composition forautomotive weather strips according to the present invention can achievestrong adhesion to the EPDM rubber without corona discharge, primerapplication or other pretreatments on the substrate surface whileexhibiting high wear resistance.

The processes for producing automotive weather strips according to thepresent invention do not require the as-applied coat to be curedcompletely in a drying oven but they permit it to be cured completely bythe heat inertia of the drying step and they can also shorten the lengthof the drying oven or lower the drying temperature. The improvement inproductivity is particularly noticeable if thermoplastic elastomers suchas TPO are used as the substrate of automotive weather strips.

The processes for producing automotive glass runs according to thepresent invention are such that by using these processes, automotiveglass runs having high wear resistance in the bottom portion whileexhibiting high softness and flexibility in the lip portions can beproduced efficiently and with minimum impact on the global environment.

While the present invention has been described in detail and withreference to specific examples thereof, it will be apparent to oneskilled in the art that various changes and modifications can be madetherein without departing from the spirit and scope thereof.

What is claimed is:
 1. A process for producing an automotive weatherstrip, comprising: applying a urethane-based aqueous paint onto asemi-finished product of an automotive weather strip; drying and curingthe paint-applied product in a heating furnace; and applying a siliconecompound having an amino group onto the semi-finished product, whereinsaid silicone compound is applied onto the urethane-based aqueous paintsurface after said drying step.
 2. The process according to claim 1,wherein said automotive weather strip has a substrate comprising athermoplastic elastomer.